1. Field of the Invention
The present invention generally relates to a write once type information recording medium such as an optical memory card. More specifically, the present invention is directed to a method and apparatus which is capable of formatting a write once type information recording medium with increasing storage efficiency, and which has the capability of correcting burst errors, to a write once type information recording medium formatted in accordance with the above-mentioned format, and to a method and apparatus for writing data to or reading data from such a write once type information recording medium.
2. Description of Related Art
The need has risen to increase data recording density in view of an economical point when data are recorded on an information recording medium. However, when the data recording density is increased, errors occurring in the reproduced data can increase because of, for instance, defects in the recording medium.
In general, to reduce errors in the reproduced data, an error correction code is added to the data during a data recording operation so as to perform the error correction. There are typically two different types of errors ocurring in the reproduced data, namely, random errors occurring at random, and burst errors occurring in a continuous manner. Once a burst error occurs, it can be hard to correct owing to a large number of continuous errors included therein.
To make error correction feasible, interleaving is carried out in a conventional information recording system. That is, a series of data is subdivided into a large number of data segments which will then be distributed in the recording medium. In this case, even if positionally continuous errors occur on the recording medium due to defects thereof, the errors are not continuous in on the reproduced data. As a result, these errors can be corrected as random errors.
FIG. 1 schematically represents an example of the conventional interleaving technique. In accordance with the conventional interleaving method, 272 "synchronization signals for a frame and bit" (simply, referred to "synchronization signals") are first arranged, each of which is composed of 8 bits, for instance, and indicated by symbol "F" as illustrated in FIG. 1. Subsequently, a 272-bit packet "a", a 272-bit packet "b", a 272-bit packet "c", - - - , a 272-bit packet "n" are arranged in parallel to each other, as illustrated in FIG. 1. The first 272-bit packet "a" contains 190-bit data consisting of a1, a2, - - - , and a190, and an 82-bit error correction code consisting of a191, a192, - - - , and a272. Similarly, the second 272-bit packet "b" contains 190-bit data consisting of b1 to b190, and an 82-bit error correction code consisting of b191 to b272, and the third 272-bit packet "c" contains 190-bit data consisting of c1 to c190, and an 82-bit error correction code consisting of c191 to c272. Also, the final 272-bit packet "n" contains 190-bit data consisting of n1 to n190, and an 82-bit error correction code consisting of n191 to n272.
The 8-bit synchronization signals and the plurality of packets, which have been arranged in the above-described manner, are read in the direction indicated by arrows shown in FIG. 3 as follows. The reading operation is carried out sequentially from the synchronization signal F, the first bit al of the first packet "a", the first bit b1 of the second packet "b" the first bit c1 of the third packet "c" and up to the first bit n1 of the last packet "n". Next, the reading operation is performed sequentially from the synchronization signal F, the second bit a2 of the first packet "a", the second bit b2 of the second packet "b" the second bit c2 of the third packet "c", and up to the second bit n2 of the final packet "n". In this reading manner, the packets up to the 272-nd bit n272 of the last packet "n" are read out, and then they are rearranged as a bit stream as shown in FIG. 2. Conventionally, such a rearranged bit stream is recorded on the information recording medium.
The bit stream, beginning from the synchronization signal "F" through a1 to n272, as shown in FIG. 2 is called a "sector". In the conventional recording medium with the above described recording format, the larger the number of interleaving processes becomes (namely, the greater the quantity of packets becomes), the more error correction can be performed with respect to the burst error. However, the increasing number of interleaving processes requires a longer sector. Since various lengths of data are normally recorded in a single sector, a long sector may include a useless (unused) storage capacity in case of short (small) data. Consider now the case where short data having three packets is stored into a long (large) sector. As shown in FIG. 3, even if (272.times.(8+3) bits data from F, a1, b1, c1, F, a2, b2, c2, - - - , up to F, a272, b272 and c272 is recorded in this large sector, a substantial sector portion will remain as a "nonrecorded portion". Furthermore, if the fourth packet d1, d2, - - - , d272 is to be additionally recorded into this large sector, although the bit "d1" should be originally interleaved between the above bit c1 and the synchronization signal F, this bit "d1" cannot be inserted between c1 and F since the bit c1 and the synchronization signal F are consecutive. Similarly, the second bit "d2" of the fourth packet cannot be inserted between the bit c2 and the synchronization signal F.
Although the overall portion of one sector may be rewritten in a rewritable type information recording medium, additional recording becomes practically difficult in the case of a write once type information recording medium. Furthermore, additional writing of information into a non-recorded portion will reduce the error correction capability as compared with the case wherein all frames of this recording medium are originally interleaved to be stored. This is because a single sector will be divided into more than two groups in such a case, and hence, the total number of interleaving processes is decreased.
As previously described, the conventional data recording medium posses a trade-off problem in that if a sector is set long, the useless unrecorded portion is increased, and therefore the recording efficiency is lowered, whereas if a sector is set short, the error correction capability is reduced.